Re-use variables/objects in callbacks

Question

Re-use variables/objects in callbacks

I was wondering this, in the following example, what would be the best way to handle re-use my helpers object?

var test = {
  Projects: 'an object goes here',
  helpers: require('../helpers'),

  test: function(req, res) {
    if (this.helpers.is_post(req)) {
      // tried this
      var test = this.helpers;

      this.Projects.byCode(req.params.project_code, function(project) {
        if (!project) {
          this.helpers.flash(req, 'error', 'Unable to find project.');
          // tried this
          helpers.flash(req, 'error', 'Unable to find project.');
          res.redirect('/projects');
        }
      });
    }
  }
};

I know I can't re-use variables, objects, etc in callbacks since they're not execute during the same runtime, but still there must be some kind of better/clearer way of doing such a thing?

Even if I tried to reassign this.helpers to another variable, it gives me errors saying that it is undefined.

Thanks!

javascript
node.js
callback

Answer 1

Why do you think you cannot re-use variables inside callbacks? They are executing not only in the same runtime, but in the same thread! That's the beauty of JavaScript.

Instead, your problem is likely a misuse of this. For example, it will definitely not work without the assignment to var test = this.helpers. And even that won't work if you call the method like so:

var testIt = test.test;
testIt(req, res);

Try something like the following instead:

var helpers = require('../helpers');

var test = {
  Projects: 'an object goes here',

  test: function(req, res) {
    if (helpers.is_post(req)) {
      this.Projects.byCode(req.params.project_code, function(project) {
        if (!project) {
          helpers.flash(req, 'error', 'Unable to find project.');
          res.redirect('/projects');
        }
      });
    }
  }
};

It's really pretty nonsensical to put an entire module as a property of your object, anyway.